(CNN) President Donald Trump's pardon of former Sheriff Joe Arpaio has been widely denounced as another instance of the President's scorn for the judiciary. Yet one set of voices has been missing: that of Chief Justice John Roberts and the nation's leading judges.

They have been silent since the beginning, when Trump derided a judge of Mexican heritage during the 2016 presidential campaign and during the furor over an immigrant travel ban early in his presidency when he referred to a "so-called judge."

That pattern held after Trump's repudiation Friday of a US district court judge's conviction of Arpaio for criminal contempt. The July 31 conviction arose from Arpaio's flagrant defiance of another judge's orders in a long-running case over the former Maricopa County sheriff's targeting of Latinos in Arizona.

Trump's pardon for Arpaio negated the findings that Arpaio -- a law enforcement officer -- violated constitutional rights with his racial-profiling practices. When ordered to stop detaining Latino drivers unless there was reason to suspect they had committed a crime, Arpaio refused.

That's what makes the current silence in the judiciary especially notable. Arpaio was not convicted of routine criminal misconduct; his disobedience directly challenged judicial integrity and independence.

Leaders in Congress, including Republican House Speaker Paul Ryan,as well as the American Bar Association and civil rights groups blasted Trump's move. Many critics focused on his evident disdain for the judiciary.

"The crime that Arpaio was convicted of committing -- criminal contempt of court for ignoring a judge's order -- showed a blatant disregard for the authority of the judiciary," ABA President Hilarie Bass said in a statement Friday. "Granting Arpaio an expedited pardon sends the wrong message to the public."

Bass and other legal experts have noted that the President has broad pardon powers but say in this situation Trump could be undercutting the public's faith in the judicial system.

Chief Justice John Roberts had no comment, according to Supreme Court public information officer Kathy Arberg.

Judges on the US district and appeals courts often look to the Supreme Court for guidance. The nine who sit atop the three-tiered federal bench have not voiced their views of Trump since he took office in January. By his conduct, Roberts appears to be signaling that judges should hold off.

A delicate balance of powers

To be sure, members of the federal bench -- appointed for life -- often navigate a difficult line in the separation of powers. They try to avoid actions that might be regarded as joining the political fray or interfering with the two other branches.

Still, Trump's efforts to influence legal proceedings seem to be mounting. His flouting of the judiciary comes as he has also tried to discredit Attorney General Jeff Sessions and the officials leading a Russia investigation related to the 2016 presidential election. Trump fired FBI Director James Comey and has criticized then-acting FBI Director Andrew McCabe and special counsel Robert Mueller, who is investigating whether anyone in the Trump campaign colluded with Russia to influence the election.

In contrast to Roberts' silence, there were times when Chief Justice William Rehnquist, who led the court from 1986 until his 2005 death, publicly defended the judiciary.

During the 1996 presidential election, politicians including Republican nominee Bob Dole lambasted US district court Judge Harold Baer of New York for excluding evidence from a drug case that had been seized by police under questionable circumstances. President Bill Clinton, running for reelection, signaled he might consider asking for Baer's resignation. Other critics called for Baer's impeachment.

In a speech at the time, Rehnquist said impeachment should be reserved for criminal misconduct and called the independence of the judiciary "one of the crown jewels of our system of government." US Appeals Court Judge Jon Newman, then chief judge of the circuit covering New York, said in a statement that the political attacks on Baer had "gone too far," amounting to "extraordinary intimidation."

Pardoning Arpaio

In the Arpaio matter, CNN and other news organizations have learned that Trump earlier had asked Sessions whether the criminal contempt trial against Arpaio could be stopped. He was rebuffed, according to accounts first reported by The Washington Post.

Arpaio was convicted for willfully disobeying the law after a court ordered him to stop singling out drivers based on ethnicity and detaining them without charges. Arpaio, who first took office in 1993, rose to national prominence for his crackdown on illegal immigration, earning the nickname "America's toughest sheriff" along the way.

He defied the orders of US District Court Judge G. Murray Snow to stop the racial profiling that was the subject of civil rights litigation. On July 31, when US District Court Judge Susan Bolton found Arpaio guilty of criminal contempt for disobeying Snow's orders dating to 2011, she said: "Not only did (Arpaio) abdicate responsibility, he announced to the world and to his subordinates that he was going to continue business as usual no matter who said otherwise."

When Trump pardoned Arpaio, who was an early and robust supporter of his candidacy, the President referred to Arpaio's work "protecting the public from the scourges of crime and illegal immigration." Trump made no mention of the reason for the criminal contempt finding.

Last year during the campaign, Trump disparaged US District Court Judge Gonzalo Curiel as the San Diego-based judge was hearing a fraud claim against Trump University. Trump said Curiel, born in Indiana and of Mexican heritage, would not be fair because of Trump's proposal to build a wall along the southern US border.

After he became President, Trump referred to US District Court Judge James Robart in Washington state as a "so-called judge" when Robart temporarily blocked the administration's travel ban covering certain Muslim-majority countries. Trump said that "if something happens blame him and the court system."

Such criticism prompted US Court of Appeals Judge Jay Bybee of the 9th Circuit to write, without naming Trump, "Such personal attacks treat the court as though it were merely a political forum in which bargaining, compromise, and even intimidation are accepted principles."